go/packages: issue error if 'go list' on PATH is too new

An application that links in version 1.18 of (say)
go/types cannot process Go source files reported
by version 1.19 of 'go list'. There is no way to
tell go list to behave as if it was go1.18, so
for now we proceed with parsing/typechecking but,
in case of errors, we issue an additional informative
diagnostic.

Fixes golang/go#55883
Fixes golang/go#55045
Updates golang/go#50825
Updates golang/go#52078

Change-Id: I5fd99b09742c136f4db7f71d2a75e4cdb730460d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/435356
gopls-CI: kokoro <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Alan Donovan <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>
Reviewed-by: Zvonimir Pavlinovic <[email protected]>

internal/gocommand/version.go

@@ -10,8 +10,15 @@ import (
 	"strings"
 )
 
-// GoVersion checks the go version by running "go list" with modules off.
-// It returns the X in Go 1.X.
+// GoVersion reports the minor version number of the highest release
+// tag built into the go command on the PATH.
+//
+// Note that this may be higher than the version of the go tool used
+// to build this application, and thus the versions of the standard
+// go/{scanner,parser,ast,types} packages that are linked into it.
+// In that case, callers should either downgrade to the version of
+// go used to build the application, or report an error that the
+// application is too old to use the go command on the PATH.
 func GoVersion(ctx context.Context, inv Invocation, r *Runner) (int, error) {
 	inv.Verb = "list"
 	inv.Args = []string{"-e", "-f", `{{context.ReleaseTags}}`, `--`, `unsafe`}
@@ -38,7 +45,7 @@ func GoVersion(ctx context.Context, inv Invocation, r *Runner) (int, error) {
 	if len(stdout) < 3 {
 		return 0, fmt.Errorf("bad ReleaseTags output: %q", stdout)
 	}
-	// Split up "[go1.1 go1.15]"
+	// Split up "[go1.1 go1.15]" and return highest go1.X value.
 	tags := strings.Fields(stdout[1 : len(stdout)-2])
 	for i := len(tags) - 1; i >= 0; i-- {
 		var version int